This invention relates to noise emission reduction and particularly to the reduction of noise emitted by the tower of a wind turbine.
Wind turbines conventionally comprise a tall toward of circular or polygonal cross-section with a nacelle mounted at the top, the nacelle mounting a large multi-bladed propeller rotating about the horizontal axis and connected through a system of gears to an electrical generator also contained within the nacelle, the nacelle is arranged to rotate about a vertical axis on top of the tower so as to keep the propeller disc facing into the wind. All of the parts driven by the turbine mechanically are contained within the upper nacelle and electrical power generated within the nacelle is carried down the tower and away to its destination by the cables and rotary electrical connectors.
Since the wind turbine includes a generator and associated gearing the wind turbine inevitably generates noise. Due to the necessity to place wind turbines on high windswept points and due to the fact that the noise is generated by the parts at the top of the wind turbine such noise can be a problem over a large area around the wind turbine since the noise can travel along a direct straight line path to considerable distances without encountering any absorbing obstruction.
This problem is accentuated by the fact that most wind turbines generate noise at two or more discrete frequencies which are distinctive of the wind turbine design as well as generating noise across a continuous spectrum so where a farm of a number of identical wind turbines is set up their combined noise at these discrete frequencies, being at the same frequency for all of the turbines, can carry for several miles.
It has been found that a major source of this noise is mechanical vibrations generated by the moving parts inside the nacelle which transmitted into the nacelle structure and then into the tower. This mechanical vibrations causes the tower structure to vibrate and it is this vibration of the tower structure which emits the noise.
It has been attempted to solve this problem by fitting vibrating isolating mounts between the machinery is the nacelle and the actual nacelle and tower structures but this has been fully effective in eliminating this noise.
This invention was intended to eliminate or at least reduce noise emission from wind turbine towers, but may have other applications.